<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text" id="i1">
<input type="text" id="i2">
<input type="button" value="加" onclick="f(1)">
<input type="button" value="减" onclick="f(2)">
<input type="button" value="乘" onclick="f(3)">
<input type="button" value="除" onclick="f(4)">
<div>
    结果:<span></span>
</div>

<script>
    console.log("代码执行了")
    function f(x) {
        let d = document.querySelector("span");
        let i = document.querySelector("#i1")
        let i1 = document.querySelector("#i2")
        if (isNaN(i.value)||isNaN(i1.value)){
            d.innerText = "输入错误!";
            return;
        }
        switch (x) {
            case 1:
                d.innerText = i.value*1 + i1.value*1;
                break;
            case 2:
                d.innerText = i.value - i1.value;
                break;
            case 3:
                d.innerText = i.value * i1.value;
                break;
            case 4:
                d.innerText = i.value / i1.value;
        }
    }
</script>
</body>
</html>